U.S. Pat. No. 4,777,915 describes an electromagnetic actuator for operating an engine valve of a piston-type internal-combustion engine. The actuator has two spaced electromagnets between the pole faces of which an armature is reciprocated by electromagnetic forces against the force of resetting springs. The armature is fixedly connected with the stem of the engine valve. The upper electromagnet serves as a closing magnet, whereas the lower electromagnet serves as an opening magnet so that by means of an alternating energization of the closing magnet and the opening magnet the engine valve may be closed and opened. Since, because of temperature changes and/or wear, the opening and particularly the closing conditions of the engine valve change and thus the predetermined valve lash (clearance) also changes, in such a system a piston-and-cylinder unit shifts the position of the closing magnet as dictated by operational requirements and thus the valve lash is adjusted. Such a solution, however, has the disadvantage that due to a valve lash adjustment the stroke of the setting unit, that is, the displacement of the armature between the two pole faces of the electromagnets also changes which is impermissible in case of a throttle-free load control of the internal-combustion engine, because then the charge quantities in the engine cylinder would change as a function of temperature and time.
U.S. Pat. No. 5,762,035 describes an electromagnetic actuator having a valve lash adjuster in which the electromagnets are arranged at a fixed distance from one another in a housing which also encompasses the opening spring. As a valve lash adjuster a hydraulic setting means is provided which is connected with a pressure medium supply and by means of which the housing may be shifted relative to the cylinder valve coupled with the closing spring. In this manner it is feasible to effect an adjustment (equalization) of the valve lash without changing the displacement geometry of the armature and thus the stroke of the setting device. The housing is caused to execute follow-up motions corresponding to the temperature or wear-dependent changes thus avoiding, for example, a rattling noise during operation. Such a system, however, requires a substantial structural outlay because the setting unit has to serve at the same time as a mount and guidance for the actuator housing.